(From company literature) Nikon PK-11A 8mm Auto Extension Ring. Nikon extension rings can be used singly or in combination to vary the reproduction ratio of lenses from 50 to 300mm.

They are mounted between the camera body and the lens, As a rule, the effect becomes stronger the shorter the focal length of the lens in use, and the longer the focal length of the extension ring. Through the lens (TTL) exposure control automatically compensates for lens extension.

Would you recommend the product? Yes |
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Pros:

A safety net for your AF camera, mild extension sometimes just enough

Cons:

no AF, but who cares?

I have one of these and use it more often than you might expect.

Two reasons:

First, it often adds just that little bit of extra extension needed to get tighter on a mcaro subject, but not too much, and it is very easy to carry around.

Second, it does not add much extension, and protects the delicate bits of the more modern camera mounts from possible damage that can be caused by some older accessories. I do some work with thiigs like bellows, extension tubes, and off-brand adapters of various sorts, and putting a PK-11A between these and the camera adds to my peace of mind. According to Nikon, for example, the old K extension tubes, BR tubes, etc shoud not be used with AF or digital camera because of possible damage to the various electronic and mechanical couplings in the mounts of these cameras, but with this ring between the camera and the older accessories, I can sonstruct whatever combination I need to get the image I want.

I almost never use AF for macro work anyway, so the lack of AF coupling is irrelevant.